Fish avoid visually noisy environments that reduce their perceptual abilities

The environment contains different forms of ecological noise that can reduce the ability of animals to detect information. Here we ask whether animals can adapt their behaviour to either exploit or avoid areas of their environment with increased dynamic visual noise. By immersing three-spined sticklebacks (Gasterosteus aculeatus) into environments with a simulated form of naturally occurring visual noise – light bands created by the refraction of light from surface waves termed caustic networks – we tested how such visual noise affected the movements, habitat use, and perceptual abilities of these fish. Fish avoided areas of higher visual noise, and achieved this by increasing their activity as a function of the locally perceived noise level, resulting in individuals moving away from noisier areas. By projecting virtual prey into the environment with different levels of visual noise, we found that the fish’s ability to visually detect prey decreased as visual noise increased. We found no evidence that fish increased their exploration (and decreased their refuge use) in environments with increased visual noise, which would have been predicted if they were exploiting increased visual noise to reduce their own likelihood of being detected. Our results indicate that animals can use simple behavioural strategies to mitigate the impacts of dynamic visual noise on their perceptual abilities, thereby improving their likelihood of gathering information in dynamically changing and noisy environments.

Effect of Repetitive Transcranial Magnetic Stimulation on a Target Moving in Front of a Static or Random Dynamic Visual Noise

Observers report seeing as slower a target disk moving in front of a static visual noise (SVN) background than the same object moving in front of a random dynamic visual noise (rDVN) background when the speed is the same. To investigate in which brain region (lower vs. higher visual areas) the background and the target signals might be combined to elicit this misperception, the transcranial magnetic stimulation (TMS) was delivered over the early visual cortex (V1/V2), middle temporal area (MT) and Cz (control site) while participants performed a speed discrimination task with targets moving in front of an SVN or an rDVN. Results showed that the TMS over MT reduced the perceived speed of the target moving in front of an SVN, but not when the target was moving in front of an rDVN background. Moreover, the TMS do not seem to interfere with encoding processing but more likely affected decoding processing in conditions of high uncertainty (i.e., when targets have similar speed).

Dynamic Visual Noise Does Not Affect Memory for Fonts

Dynamic visual noise (DVN) selectively impairs memory for some types of stimuli (e.g., colors, textures, concrete words), but not for others (e.g., matrices, Chinese characters, simple shapes). According to the image definition hypothesis, the key difference is whether the stimulus leads to images that are ill-defined or well-defined. The former will be affected because the addition of noise quickly reduces the usefulness of the image in supplying information about the item's identity. The image definition hypothesis predicts that fonts should lead to ill-defined images and therefore should be affected by DVN, and although three previous studies appear to show this result, they lack a key control condition and report only proportion correct. Two experiments reassessed whether DVN affects memory for fonts, but, unlike the previous studies, both included a static visual noise condition and both were analyzed using signal detection measures. There was no evidence that DVN affected memory for font information, thus disconfirming a prediction of the original version of image definition hypothesis. We suggest a revised version that focuses on redintegration can explain the results.